A compact-disk read-only memory (CD ROM) is a non-magnetic disk, typically 4.72 inches (12 centimeters) in diameter, which can store as much as 680 megabytes of data. The data can be permanently recorded onto the CD ROM by using a laser beam to burn microscopic pits into the surface. Data can be read by using a low power laser to sense the presence or absence of pits.
A CD ROM (file) server is a mass storage device that holds programs and data that can be accessed and shared by workstations connected to a local-area network. CD ROM servers typically have multiple small computer system interface (SCSI) host bus adapters and a large, external chassis which houses multiple SCSI CD ROM drives.
The CD ROM format for the distribution of large quantities of data is well known, and dedicated computer file servers having multiple CD ROM drives for online CD ROM access have become popular. Such dedicated CD ROM server subsystems, which include 40 or more CD ROM drives, have become available for this purpose.
Although CD ROM servers are capable of storing and providing access to large quantities of data, CD ROM servers have many disadvantages. For example, compared to hard disks, access times for CD ROMs are approximately 50 times longer, and data transfer times are approximately 20-30 times longer. More significantly, CD ROM drives are relatively unreliable, having, for a given period of time, approximately 10 times as many failures as any other component of the server. Furthermore, CD ROM servers consume more power and are larger and more expensive than hard disk drives.
One solution is to copy CD ROM data to a conventional file server hard disk drive array. However, when that is done, the data is no longer in a CD ROM format, but rather is formatted for a file server. Moreover, the file server format may be incompatible with the CD ROM format so that CD ROM server software, which is designed to access data from CD ROMs, may not be able to access the same data in a conventional file server format. Furthermore, such a copying operation is a manual step and the data copied to the file system must be provided as a resource on the network. These steps increase the maintenance requirements of the server and increases the likelihood for human error.
Therefore, what is needed is a CD ROM-compatible server with improved reliability and performance, and with substantially reduced power consumption, cost, and size as compared to traditional CD ROM servers.